Cluster labels are cut off on horizontal hclust dendrogram

I used hclust and as.dendogram to make a dendrogram, but when I rotate it to a horizontal orientation, the model names are cut off. How can I make sure that the plot shows the entire model names?

You need to play with the margin. Here is an example (it also uses dendextend to give extra control over the color and shape of the dendrogram)

library(dendextend)
library(dplyr)
small_mtcars <- head(mtcars) %>% select(mpg, cyl, disp)
small_mtcars

d1 = small_mtcars %>% dist() %>% hclust(method = "average") %>% as.dendrogram() 
library(colorspace)
some_colors <- rainbow_hcl(nrow(small_mtcars))
d1_col <- some_colors[order.dendrogram(d1)]
# some colors for fun
d1 <- d1     %>% 
        set("labels_cex",1.2) %>% 
        set("labels_colors", value= d1_col) %>% 
        set("leaves_pch", 19) %>%
        set("leaves_cex", 2) %>%
        set("leaves_col", value= d1_col) 

par(mfrow = c(1,2))

par(mar = c(2,2,2,2))
d1 %>% 

    plot(main="d1 (bad margins)", horiz = TRUE)

par(mar = c(2,2,2,10))
d1 %>% 
    set("labels_cex",1.2) %>% 
    plot(main="d1 (good margins)", horiz = TRUE)